True Masses of Radial-Velocity Exoplanets

Abstract

We explore the science power of space telescopes used to estimate the true masses of known radial-velocity exoplanets by means of astrometry on direct images. We translate a desired mass accuracy (+/10% in our example) into a minimum goal for the signal-to-noise ratio, which implies a minimum exposure time. When the planet is near a node, the mass measurement becomes difficult if not impossible, because the apparent separation becomes decoupled from the inclination angle of the orbit. The combination of this nodal effect with considerations of solar and anti-solar pointing restrictions, photometric and obscurational completeness, and image blurring due to orbital motion, severely limits the observing opportunities, often to only brief intervals in a five-year mission. We compare the science power of four missions, two with external star shades, EXO-S and WFIRST-S, and two with internal coronagraphs, EXO-C and WFIRST-C. The star shades out-perform the coronagraph in this science program by about a factor of three. For both coronagraphs, the input catalog includes 16 RV planets, of which EXO-C could possibly observe 10, of which 6 would have a 90% guarantee of success. Of the same 16 planets, WFIRST-C could possibly observe 12, of which 9 are guaranteed. For both star-shade missions, the input catalog includes 55 planets, of which EXO-S could possibly observe 37, of which 20 are guaranteed. Of the same 55, WFIRST-S could possibly observe 45, of which 30 are guaranteed. The longer spectroscopic exposure times should be easily accommodated for the RV planets with guaranteed success.

References in corpus (13)

• Wide-Field InfrarRed Survey Telescope-Astrophysics Focused Telescope Assets WFIRST-AFTA 2015 Report
• Observed Properties of Exoplanets: Masses, Orbits, and Metallicities
• Photometric and Obscurational Completeness
• The distribution of exoplanet masses
• New Completeness Methods for Estimating Exoplanet Discoveries by Direct Detection
• Derivation of the Mass Distribution of Extrasolar Planets with MAXLIMA - a Maximum Likelihood Algorithm
• The Posterior Distribution of sin(i) for Exoplanets with M_T sin(i) Determined from Radial Velocity Data
• Science Parametrics for Missions to Search for Earthlike Exoplanets by Direct Imaging
• Density Estimation for Projected Exoplanet Quantities
• Deriving stellar inclination of slow rotators using stellar activity
• The effects of viewing angle on the mass distribution of exoplanets
• Atmospheric characterization of cold exoplanets using a 1.5-m coronagraphic space telescope
• Photometric Orbits of Extrasolar Planets

Cited by in corpus (7)

• A Statistical Comparative Planetology Approach to the Hunt for Habitable Exoplanets and Life Beyond the Solar System
• The Direct Detectability of Giant Exoplanets in the Optical
• Catalogue of exoplanets accessible in reflected starlight to the Nancy Grace Roman Space Telescope. A population study and prospects for phase-curve measurements
• Large Interferometer For Exoplanets (LIFE). X. Detectability of currently known exoplanets and synergies with future IR/O/UV reflected-starlight imaging missions
• Optimized Bandpasses for the Habitable Worlds Observatory's ExoEarth Survey
• Improving estimates of msini by expanding RV datasets
• WFIRST-AFTA Coronagraphic Operations: Lessons Learned from the Hubble Space Telescope and the James Webb Space Telescope